NBSIR 75-797

An Evaluation of a Range-Top Warning

Light System

Mary E. Stefl J. J. Persensky

Human Factors Section

Product Systems Analysis Division

Center for Consumer Product Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

July 1975

Final Report

Prepared for Consumer Product Safety Commission

Washington, D. C. 20207

NBSIR 75-797

AN EVALUATION OF A RANGE-TOP WARNING

LIGHT SYSTEM

Mary E. Stefl

J. J. Persensky

Human Factors Section

Product Systems Analysis Division

Center for Consumer Product Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

July 1975

Final Report

Prepared for Consumer Product Safety Commission

Washington, D. C. 20207

U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton, Secretary

James A. Baker, III. Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

AX EVALUATION OF A RANGE-TOP WARNING LIGHT SYSTEM

1 . 0 INTRODUCTION

During fiscal 1974, 401 In-Depth Investigation Reports (IDIR's)

involving range-related accidents were obtained from the Consumer Product

Safety Commission (CPSC) for the CPSC-funded "Appliances" project.

The Human Factors Laboratory staff of the National Bureau of Standards

(NBS) reviewed these reports in order to identify any systematic relationship (s)

between injuries, hazards, and user activity sequences.-'- CPSC also

asked NBS to suggest countermeasures designed to reduce the number

and severity of appliance-related accidents and to investigate the

feasibility of such countermeasures

.

One accident sequence to emerge from the IDIR analysis concerned

injuries to range users who were unaware that one or more of the surface

units was activated . This problem occurred mainly with electric ranges

,

and proposed solutions to it have focused on increasing the user's

awareness of surface unit activation. The use of warning lights has

been recommended by both Underwriter ' s Laboratory (UL) and NBS. Specifically,

UL has proposed that a signal lamp indicating burner activation be

clearly visible to a person standing directly in front of and 10 feet

from the range. A viewing elevation of five feet with a standard-size

pan positioned on the burner surface was specified.'- The positioning

of the signal light or lights in relation to the surface unit controls,

however, was not specified so that a single warning light, regardless

of its position, can fulfill the requirements of the proposed standard.

In contrast, the former NBS Office of Flammable Fabrics recommended

that indicators be provided which unequivocally denote for the user

which surface element is energized.-^ This may be done by providing

a separate signal light for each element and by positioning each light

adjacent to the control for that element.

The proposed UL standard does not consider the activities of the

range user. Kitchen tasks vary with respect to cognitive content,

i.e., different kitchen tasks require varying degrees of concentration

(Steidl, 1972). This point is important because the ability to distract

someone from a task is related in a complex way to the "demandingness",

or cognitive content, of the task (Fitts and Posner, 1967). Two possible

outcomes may occur when individuals perform a highly cognitive task.

Detailed results of the accident analysis effort will be presented in the

Final Report for the project.

^oposed Amendments to UL Standard No. 858, "Household Electric Appliances,"

February 1, 1974.

^Letter from Sidney Greenfield, NBS , to Walter Kirk, American Gas

Association Labs, Inc., January 2, 1973.
They may become so engrossed in that task that their susceptability

to a distraction, such as a warning signal, is inhibited. Or, the

performance of that demanding task may instead serve to attune their

perceptual capabilities and actually enhance their responsiveness to

a warning stimulus. How the effectiveness of any given alerting system

relates to task content cannot be accurately predicted without empirical

test.

The present study evaluated a user alerting system in terms of

the cognitive content of the range user's activity as well as certain

attributes of the display which could influence the response of the

visual system. These physical variables were to include signal light

intensity, surround color, and signal light position on the range top.

For reasons to be discussed later, signal light intensity could not

be varied independently.

An alerting system of warning lights was studied since this was

the system recommended by both ITL and NBS, as well as the one most often

employed by range manufacturers at the present time. In accordance

with the NBS recommendation, a system was studied which provided a separate

warning light for each of the usual four range burners.

The present study was limited in scope. It was not an attempt

to design an "optimal" alerting system. To have done so would have

involved the evaluation of other types of systems , many of which would

be of limited acceptability to users and/or manufacturers. Other potentially

important factors, including kitchen configuration and the position

of the user in relationship to the range, were also excluded from the

present investigation.

2 . 0 METHODOLOGY

2.1 Design

In the present study, both warning light color and ambient lighting

were lie Id constant. Red was selected as the most appropriate color

since, according to current military and industrial standards, it signifies

alert or warning (Woodson fT Gonover, 1964). Ambient lighting was set

at 50 footcandles as this is the level generally recommended for kitchens

(Kaufman, 1966; Woodson § Gonover, 1964).

Warning light position was varied. The warning lights were positioned

next to each of four control knobs on a moveable control panel. This

panel could be fitted into any one of four positions on the range stimulator

as Figure 1 illustrates. The panel positions employed were based on

a review of currently available range designs and included warning lights

adjacent to controls located on:

1 . the front of the range , perpendicular to the cooking surface

(Front Perpendicular)

;

2. the front of the range, parallel to the cooking surface (Front

Parallel)

;
e@©0
3. the side of the range, parallel to the cooking surface (Side

Parallel) ; and

4. the back (back-splash) of the range, perpendicular to the cooking

surface (Back Perpendicular)

.

Other warning light systems were considered (e.g., lights adjacent to

the surface element) but were not included in the study as their implementation

would involve practical problems or major changes in range design.

The background against which the signal lights were fitted was

also varied. Informal surveys conducted in (a) local homes and apartments

and (b) local retail outlets revealed that control knobs and warning

lights are generally fitted against either a dark, flat surface (brown

or black) or a chromed, reflective surface.

Research on visual perception (e.g., Geldard, 1972) indicates that

the contrast ratio between the brightness of the stimulus (warning light)

and its surround (background panel) is more relevant than background

color in terms of the psychophysical response characteristics of the

human eye . However , controlling contrast ratio would involve controlling

the ambient light conditions at each of the four experimental rangetop warning light positions ; such precision was not feasible in the

present experimental situation. Furthermore, controlled light conditions

do not exist in real kitchens where contrast ratios vary as a function

of the time of day, the type of day (sunny or cloudy) , the position

of the observer, and so on. In the present study the background color

against which the lights were fitted was varied systematically recognizing

that the actual contrast ratios were thus undefined and represent a possible confounding variable. Two backgrounds were employed: a flat,

black surface and a chromed, reflective surface.

Finally, two levels of task demand were employed. Working a jigsaw

puzzle was chosen as a high cognitive task, analogous to kitchen tasks

like cooking or meal planning. Sorting beans into four different receptacles

was chosen as a low cognitive task, analogous to washing dishes or chopping

vegetables. That the cognitive content of the analogous kitchen tasks

varies has been validated by subjects' ratings in a study by Steidl

(1972).

Practical considerations interfered with an original intention

to treat warning light intensity as an independent variable. Actual

range -top warning lights had been provided by a range manufacturer for use in

the study. When measured in the NBS laboratory, however, the intensity

ranges of these lights were found to differ widely. The experimental,

apparatus had been fitted with a single rheostat; because of this limitation,

a single rheostat setting produced a different stimulus intensity in

each of the four lights. Rather than employ a generically different

type of light whose intensities could be more closely matched, the actual

warning lights were used for their face validity and authenticity. In

the present study, then, warning light intensity was varied, but not

in a uniform manner.

4
The two surround colors, four warning light positions, and two

types of tasks combined factorial ly to produce a total of 16 unique

stimulus conditions. A repeated measures design was employed, that

is, each subject participated in all of the stimulus conditions.

2 . 2 Apparatus

A mock range top was constructed for use in the study. In accordance

with averages observed in local retail outlets, it measured 30 inches

(76.20 cm) across and 23 inches (58.42 cm) deep, and contained three

6-inch (15.24 cm) diameter heating units and a fourth 8-inch (20.32 cm)

heating unit in the right front position (see Figure 1) . It was finished

with a white surface since white, according to range salesmen, is the

most popular range color. Non- functional heating units were obtained

from old ranges and mounted on the range top . Each element was equipped

with a switch which, when depressed, deactivated the corresponding

pilot light.

A separately constructed control panel could be mounted in each

of the four specified positions: Front Paralled, Front Perpendicular,

Side Parallel, and Back Perpendicular, as indicated in Figure 1. The

four warning lights were back-mounted to the panel so that a 3/8-inch

(0.95 cm) square was visible to the observer. Xon- functional control

knobs were mounted leneath each light. The panel was constructed of

a chromed, reflective surface, hut a flat, Mack surface could be affixed

without obscuring either the warning lights or control knobs.

Pilot light intensity was measured in a darkened room by a Spectra

Pritchard spot photometer . As noted above , the high variability of

individual lights coupled with a limited experimental apparatus did

not permit the uniform variation of warning light intensity. However,

high, medium, and low intensity "ranges" were set; the average individual

intensity readings, in nits (candelas per square meter), are presented

for each light at each intensity range in Table 1. Each point represents

the average of four intensity readings. In all cases, a readily perceivable

difference existed between each intensity range for each light.

Each of the pilot lights was connected to the experimenter's console.

This console contained a digital timer and controls which activated

the lights and set light intensity. Activation of any of the four

lights started the timer; the subject's closing of the switch on the

range-top element deactivated it. Finally a clock timer was used to

measure the interstimulus interval (ISI)

.

";ile the experiment itself was conducted in a physical science

laboratory module at XBS, attempts were made to simulate a "typical"

kitchen. One of the problems of the proposed IT standard was that it

had not considered adequately typical kitchen design or use patterns.

It had specified that the proposed warning light be visible from a

5
TABLE 1

Intensity of Individual Warning Lights (in Nits)

as a Function of Intensity Range Setting

Intensity Ran£

Light Low* Medium* High*

1 12.37 38.60 45.17

2 25.50 77.90 95.60

3 43.27 128.75 160.92

4 20.50 64.50 77.87

6
viewing distance of 10 feet, but typical kitchen design does not usually

permit such viewing conditions. A small informal survey conducted

by NBS personnel in local home and apartment kitchens revealed that,

in 10 out of 12 cases, work spaces were located adjacent to, not in

front of, the range.

During the survey, measurements of work spaces, distance from

work spaces to the range, counter heights, and so forth, as well as simple "layout" diagrams were made for each kitchen. Based on these

data, the laboratory subjects were provided with a work space and range

height of 36 inches (91.44 cm). For convenience, the range simulator was situated to the left of the work space since the survey data had

shown no preference for side. The distance from the center of the

work space to the edge of the range measured 20 inches (50.80 cm).

Subjects stood while working.

Movable partitions separated the subjects' area from the control

area. A closed circuit TV camera was mounted in the far corner of

the room and focused on the subject. All the subjects' activities

were observed on a monitor in the control area. The experimenter was also within easy voice range of the subject.

A portable AM radio was operated whenever data were being collected.

This not only masked background and equipment noise which might serve

as potential cues to the subject, but also provided diversion and helped

reduce boredom.

2.3 Subjects

Eight women, ranging in age from 21 to 58 and naive to the purposes

of the study, served as subjects and were paid for their participation.

All had 20/40 vision or better as measured by a standard Snellen acuity

chart. Subjects who normally wore glasses were requested to do so both during the acuity test and the experiment itself.

2.4 Procedure

Once in the laboratory, subjects were tested for binocular visual

acuity. They were then read a standard set of instructions; these

instructions are included as an Appendix to this report.

Subjects were informed that the purpose of the research was to

study cooking behavior. They were asked to perform two different types

of tasks, a "thinking" task and a "manual" task (high and low cognitive

task content, respectively). The "thinking" task involved working

a jigsaw puzzle in the work space next to the range. This task was described as analogous to following a recipe while cooking. The "manual"

7
task, described as analogous to chopping vegetables, involved sorting

four different types of beans into four different containers. Subjects

were informed that they would be told which task to perform at any

given time.

They were further instructed that they would be distracted during

their performance, that is, from time to time, one of the four red

signal lights would come on. Whenever they noticed that one of the

lights was activated, they were to quickly pick up one of the four

bean containers and place it on the corresponding range top element.

This action would deactivate the light, and the subject could then

remove the container and resume her task.

The problems involved with controlling warning light intensity

were noted above. Because lamp intensity was not uniform at a particular

range setting, it could not be considered an independent variable in

the data analysis. For procedural purposes only, however, the three

stimulus ranges were combined factorially with the four warning light

positions and two background colors to produce 24 different experimental

conditions. These conditions were administered in a different random

order to each subject. Randomization helped control transfer and/or

learning effects. Within each condition, half of the session was

devoted to the puzzle task and the other half to the bean sorting task.

Subjects switched tasks on verbal command from the experimenter.

Each session lasted 48 minutes and consisted of 16 experimental

trials or signal light activations. Exactly half of the activations

occurred during each task. During a given session, each of the four

signal lights was activated four times, but the order of activation

was random. Interstimulus interval (ISI) was also varied randomly.

Four different ISI values were employed, ranging from one to five minutes,

with a mean of three minutes.

In order to familiarize subjects with the experimental set-up,

four practice trials were administered on the first day. Thereafter,

each subject participated in a total of four 48 -minute experimental

sessions on each of six days. Following each session, subjects were

given a short break during which time they could walk around or leave

the experimental room. The experimenter used this time to change the

control panel position or background color when appropriate. Thus,

each day's session lasted approximately four hours.

A typical experimental trial is described as follows. The experimenter,

seated out of the subject's view, activated one of the four warning

lights according to a predetermined random time interval and light

position schedule. At the same time, a digital timer was activated

and the experimenter reset the clock timer to the ISI appropriate for

the next trial. Once the subject noted the light's activation, she

picked up one of the bean containers and placed it on the burner corresponding

to the activated light. This action turned off the light and stopped

the digital timer. The experimenter then recorded the subject's reaction

8
time to the light and reset the digital timer. Concurrently, the subject

removed the container from the burner and resumed her task. Thus, a modified type of vigilance task was created, with reaction time measures

as the dependent variable.

A high degree of variability was observed in the data. The overall

mean reaction time was 7.9 sec. with a standard deviation of 5.2 seconds.

In addition, some 135 scores, or more than four percent of the total,

fell three standard deviation units or more above the individual subject

means, indicating a definite positive skew. Since most statistical

tests assume a normal distribution of scores , a logarithmic transformation

was used to normalize the data. Each score, X, was converted to X'

by means of the formula:

According to Kirk (1968), log transformation of data is often appropriate

when the dependent variable is reaction time and the data are positively

skewed

.

Mean transformed scores were then computed for each subject in

each of the 16 experimental conditions formed by the factorial combination

of four warning light positions , two background colors , and two task

types . Since means were computed across the three intensity ranges

,

each mean represented 24 converted reaction time scores. These means were then submitted to a three-way analysis of variance for repeated

measures designs.

The results of this analysis are presented in Table 2. A significant

effect (F = 21.50, df = 1,7, p < 0.005) was found for task type indicating

that tasks high in cognitive content produced reliably longer reaction

times than tasks of low cognitive content. The median reaction time scores for each subject are presented in Table 3 as a function of task

type. Median scores are used since they provide the best index of central

tendency when the original distribution of scores is skewed.

In addition, a significant effect was found for warning light position

(F = 3.16, df = 3, 21, p < 0.05). The group sums of the transformed

reaction time scores associated with each of the four range-top positions

are presented below:

Since a significant F ratio only indicates that a difference exists

between groups, Duncan's Xew Multiple Range Test was employed to determine

where the difference or differences lie. The results of this test

3 . 0 RESULTS

Front Parallel

Front Perpendicular

Back Perpendicular

Side Parallel

26.2

25.7

25.2

23.1

9
TABLE 2

Summary Table

Analysis of Variance

Transformed Scores

Source

Subj ects

A (Position)

AxS

B (Background)

BxS

C (Task)

CxS

AxB

AxBxC

AxC

AxCxS

BxC

BxCxS

AxBxC

AxBxCxS

TOTAL

SS

2.34

.18

.39

.00

.05

.43

.14

.00

.18

.01

.16

.00

.01

.01

.09

3.99

df

73

21

1

7

173

21

3

21

17

3

21

127

MS

,060

,019

000

,007

,430

,020

,000

009

,003

,008

,000

001

,003

004

3.16*

0

21.50**

0

<1

0

<1

* p < .05 ** p < .005

10
TABLE 3

vedian Reaction Tines (seconds) for

Each Subject as a Function of Task Type

Task Type

Low Cognitive High Cognitive

Subject (Bean Sorting) (Puzzle)

1 4.0 5.0

2 4.4 5.2

3 3.7 5.6

4 4.5 4.8

5 4.8 5.8

6 4.8 6.3

7 9.7 20.1

8 5.6 6.0

All Subjects

Combined 4.8 5.9

11
are shown in Table 4. They indicate that the scores associated with

both the Front Parallel and Front Perpendicular positions were

significantly longer than those associated with the Side Parallel position.

No other significant differences were observed.

Background color was not found to influence reaction time. The

mean transformed scores associated with the chrome and dark backgrounds

were, in fact, identical. None of the interaction terms approached

statistical significance.

As discussed earlier, warning light intensity was not varied uniformly

in the present study. Instead, intensity ranges were set that encompassed

the 16 different intensity values presented in Table 1. Note that

they cover a wide range - from a low value of 12.37 nits on Light 1 to a high of 160.92 nits for Light 3. Subjects' mean transformed responses

to these designated intensity values were compared by a simple t-test

for dependent groups. They were not shown to differ significantly

(t = 1.67, df = 7)

.

4.0 DISCUSSION

The present study demonstrates that the activity of the range

user can appreciably affect his or her response to an alerting system.

Subjects performing the task high in cognitive content produced generally

higher reaction times, i.e., they were less easily distracted from

their task by a warning light signal. Conversely, subjects performing

tasks low in cognitive content were more responsive to the distraction

of the warning light.

From a theoretical standpoint, these results support the notion

presented earlier that high task involvement tends to filter out or obscure low levels of external stimulation which are extraneous to

the task at hand. Housewives have indicated preferences for those kitchen

tasks which they also rate high in cognitive content (Steidl, 1972).

The current results suggest that high cognitive tasks also produce

slower response times to distracting stimuli. Thus, these preferred

tasks are potentially more hazardous, as the performer of a high cognitive

task may be less responsive to the visual cues signalling a potential

accident.

An interpretation of the significant Position effect is not so straightforward. Subjects' response times were briefest to warning

lights in the Side position. These responses were significantly briefer

than those associated with both the Front Perpendicular and Parallel

positions but no other significant differences were found.

Part of the superiority of the Side Position must be attributed

to proximity; as shown in Figure 1, this is the range-top position

nearest to the subject's work space. Field of view must also be considered.

To perform the required tasks, subjects stood facing the counter adjacent

12
TABLE 4

Duncan's New Multiple Range Test

Comparing Differences Between Group Sums

For the Position Variable

(Transformed Scores)

Side Back Front Front

Parallel Perp . Perp. Parallel

ZX^ £X^

ZX

3

= 23.1 --- 2.1 2.6* 3.1 5

EX

4 = 25.2 .5 1.0

HL = 25.7 .5

ZX

2 =26.2

* p < .05

13
to the mock range. Assuming the "normal" eye and head movements associated

with performing the tasks, the chances were small that either Front

position would be within the subjects' central visual field. On the

other hand, the two positions to which the subjects responded most rapidly,

the Side and Back, would more likely fall within the central field of

view.

The importance of viewing angle with respect to the psychophysical

response characteristics of the human eye is well documented (e.g.

,

Geldard, 1972). The image of a warning light viewed directly will fall on the central (foveal) area of the eye's retina; in this region visual

acuity and color sensitivity is maximal. On the other hand, the image

of a warning light viewed at an angle may fall on the peripheral region

of the retina. This region contains far fewer color receptors but is

maximally sensitive to low levels of illumination.

The intent here is not to dismiss the obtained results as experimental

artifact, for the laboratory set-up was patterned after observed kitchen

design. The real implication may be that warning lights should be positioned

as close to the work space, and hence to the observer, as possible,

which might require "custom fitting" a range's control panel to individual

kitchens

.

The other systems variables under study, warning light surround

and intensity, were not shown to significantly influence subjects'

reaction times. Nor were any significant interactions among variables

observed. The failure to obtain significant differences should not,

however, be equated with negative results. Instead, the failure of

these variables to influence performance may indicate that, within limits,

they need not be considered as differentially affecting safety in the

design of future warning light systems. (This statement requires further

qualification regarding warning light intensity and contrast ratio which

were not systematically varied in the present study.)

Significant differences were found in the present study; thus, some interpretation of these differences beyond the experimental laboratory

must be attempted. Consider, for example, the task variable. The

observed median reaction times for the high and low cognitive tasks

were 5.9 and 4.8 seconds, respectively. This is a relatively small,

although statistically significant, difference. In most cases, a surface

element which is unknowingly activated this additional 1.1 seconds has

little impact. In certain circumstances, however, so short a time frame

could precipitate an accident. The flammability of certain fabrics^

is within these limits and sufficient time is available for a child to

make contact with an exposed and energized burner.

The accident sequence of concern in the present study involved adult range

users injured while unaware that a surface element was activated; children,

therefore, were not included as subjects. Young children frequently incur

contact burns when crawling on a range top, but it is doubtful that 'a system of warning lights is the appropriate deterrent for such behaviors.

14
Another significant aspect of the present study is its support

of a human factors approach to safety programs. The results clearly

point to the significance of the human using the system; not only were

the tasks performed by the user found to influence reaction times , but

the physical location of the observer in relationship to the alerting

system was relevant as well. The writers of future performance standards

should not ignore this interaction between a system and its user. To

consider the psychophysical capabilities and limitations of that user

is not enough. The user's behavior must be assessed as he or she actively

interfaces with the system in question and performs the usual tasks

related to it.

Finally, certain inadequacies of the present study should be examined.

For example, despite efforts to simulate an average kitchen, post -experimental

interviews with subjects indicated that the laboratory atmosphere was

not completely dispelled. Instead of preparing food, subjects were

performing seemingly nonsensical tasks and occasionally placing a pan

of beans on a mock range top. Instead of being in a real kitchen with

freedom to move from counter to sink to range, they stood for 48 -minute

sessions at a mock-up counter in front of walls which, though decorated

with posters, were metal. In a few instances, subjects seemed genuinely

engrossed in their tasks (several reaction times of one minute or more

were found) , but it is likely that most of their attention was directed

towards monitoring the warning lights. The influence of factors such

as these on subjects' behavior should not be ignored.

5.0 METHODOLOGICAL NOTE

The exploratory nature of this study should be noted. The application

of human factors psychology to product safety has typically taken one of two forms. Precise, objective, and quantifiable dependent measures

have been collected from subjects in a rigorously controlled laboratory

setting where tasks are contrived to simulate real-world activities.

Or, observations have been made of subjects performing real tasks in

natural situations and surroundings. In this latter case, data collection

has often been limited to rather global descriptions of activity sequences

or discrete check lists where the presence or absence of certain preestablished behaviors is noted.

Compromise is inherent in choosing one of these methodologies over

the other. One method provides easily- analyzable data; the other insures

greater face validity or correspondence with the "real world."

The present study may be viewed as a first step towards merging

these two extremes to apply a methodology which uses objective, quantifiable

measures to study natural behavior. Specifically, the present study

attempted to increase the face validity of a study in a laboratory setting

by simulating real surroundings and tasks.

15
Given that the present attempt to simulate real -world surrounding

in the laboratory was moderately successful, the validity of such an

approach is not universally accepted. Chapanis (1967), for instance,

contends that the subjects' awareness that they are participating in

an experiment can never be removed. Furthermore, this awareness constitutes

only a small portion of the multitude of environmental , psychological

,

and physiological variables that influence behavior at any point in

time. The laboratory study generally manipulates three or four of

these variables, attempts to hold constant several others, but must

ignore the vast and largely unspecified remainder that continue to

influence performance in unidentified ways

.

The obvious solution, of course, is to collect data only in real

surroundings. For the present study, volunteer households might have

been found where range-top warning lights could have been instrumented

to occasionally activate during kitchen use. However, time, money

and a multitude of logistical problems make this type of naturalistic

solution untenable.

A compromise solution could involve interfacing a study of warning

lights with another of the observational studies to be conducted in

the new human factors research facility kitchen. That is, concurrent

with a study of cooking behavior, a range-top warning light or system

of lights could be instrumented to "spontaneously" activate once or twice during any given subject's experimental session. In this manner,

subjects would in no way be attuned to the activation of a warning

light; their main task, in fact, would be to prepare food. Any desired

parameters relating to the physical set-up of the range could be varied

between subjects.

16
REFERENCES

Chapanis , A. The relevance of laboratory studies to practical

situations. Ergonomics , 1967, 10 (5), pp. 557-577.

Fitts, Paul M. and Posner, Michael I. Human Performance . Belmont,

California: Brooks /Cole Publishing Company, 1967.

Geldard, Frank A. The Human Senses , Second edition. New York:

John Wiley and Sons, Inc., 1972.

Kaufman, John E. , editor. IES Lighting Handbook . New York:

Illuminating Engineering Society, 1966.

Kirk, Roger E. Experimental design . Procedures for the behavioral

sciences . Belmont, California: Brooks /Cole Publishing Company

,

Steidl , Rose . Difficulty factors in homemaking tasks : Implications

for environmental design. Human Factors , 1972, 14_ (5), pp. 471-482.

Woodson, Wesley E. and Conover, Donald W. Human engineering guide for

Equipment Designers . Berkeley: University of California Press, 1964.

17

Appendix - Instructions to Subjects

19

APPENDIX

INSTRUCTIONS TO SUBJECTS

We're trying to find out something about how people behave when

they're cooking. We think that using a kitchen involves two main

types of activities or tasks - manual tasks and so-called "thinking"

tasks. For example, one manual activity would be chopping vegetables.

A "thinking" activity would be reading and following a recipe. We

realize that preparing a meal involves both "manual" and "thinking"

activities, and we'd like to be able to find out some of the differences,

if any, between them.

Since we don't have a real kitchen, we're going to ask you to

do some other tasks which we feel fit into the categories of "manual"

and "thinking." The manual task involves bean sorting - as you can

see, the beans are here in this pot (indicate) . The thinking task

involves putting together one of the jigsaw puzzles sitting on that

table (indicate)

.

First, let's talk about the bean sorting, or manual, task. As

you can see, there are four different colors of beans. There are also

four pans, each of which is labeled with a different colored bean.

Once you're asked to begin, we'd like you to start taking beans from

the large pot and dividing them by color into the four smaller pans.

In other words, put the white beans in the pot labeled with the white

bean, the brown beans in the pot labeled with the brown bean, and so

on. Once a small pan becomes filled, simply empty all sorted beans

into this larger empty pot (indicate) . There is no need to hurry at

this task. We just ask you to work at a steady pace, as though you

were preparing an unrushed meal at home.

The thinking task involves working a jigsaw puzzle. There are

a number of different puzzles on this table - you should pick one that

you think you can put together in a couple of hours. Again, we don't

want you to hurry - instead, it's important to work at a steady pace

as you often would in your own kitchen.

During each session, you'll spend half of your time sorting beans

and the other half working on the puzzle. At the beginning of each

session, I'll tell you which of the two tasks you are to start with.

Sometimes you'll start sorting beans; other times you'll start out

working the puzzle. Later on in the session, I'll tell you when to

switch tasks

.

At the same time you're working with one of these tasks, some distractions will interrupt your work. These distractors will involve

the mock range top you see here (indicate) . As you can see, the range

has the usual four burners, four control knobs, and an indicator light

21
next to each control knob. From time to time, one of these indicator

lights will distract you by lighting up, like this (turn one light

on) . Each time you see one of the lights come on, you are to turn it

off by putting one of the pans - it doesn't matter which one - on the

appropriate burner, like this (put pan on burner). Once you place

a pan on the appropriate burner, the light will go off. As soon as

the light is turned off, count to three slowly and then remove the

pan and resume whichever of the two tasks you were involved in before

you noticed the light coming on. Before you start, you'll have some time to practice so that you can learn which burner goes with which

knob and which light.

This can get pretty complicated, so let's go over it all again.

You'll be working - at a steady and relaxed rate - on either a puzzle

or at sorting beans; that is, at either a manual or a thinking task.

You'll be told at the beginning of each session which task you're to

start with, and then later in the session when to switch activities.

As you're working, you'll be asked to watch for distractions - just

as you would at home while preparing a meal . In this case , the distraction

will be an indicator light on the range top. It's important that you

notice whenever one of the lights comes on, but you should not be watching so intently that you neglect performing one of the tasks. As soon

as you do notice a light on, you are to turn it off by placing any

one of the small pans on the appropriate burner. Once the light is

off, you can resume your main job of sorting beans or working the puzzle.

You'll be participating in this project for six days for about

four hours a day. Periodically, we'll take short 10-minute breaks.

I'll be sitting here behind the screen if you have any problems. Do

you have any questions now before we begin?

22
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. PUBLICATION OR REPORT NO. 2. Gov't Accession

sheet NBSIR 75-797

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

AN EVALUATION OF A RANGE-TOP WARNING LIGHT SYSTEM

5. Publication Date July 1975

6. Performing Organization ( ode

7 AT ITUHD

Mary E. Stefl, J.J. Persenskv

Oil, * /"\ 1 1 XI o. Performing Organ. Report No. NBSIR 75-797

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4414121

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Consumer Product Safety Commission

Washington, D.C. 20207

13. Type of Report & Period Covered

Final

14» sponsoring Agency Clodc

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

A descriptive analysis of In-Depth Injury Investigations of range-related

accidents revealed a series of incidents where range-users were unaware that

surface elements were energized. One proposed solution to this problem involved

a system of four warning lights to indicate individual surface unit activation.

A laboratory study using human subjects evaluated the effectiveness of such a system. The backgrounds against which the warning lights were fitted and the

intensity of the lights were not shown to influence subjects' responses in a reaction time task; however, the position of the lights and the type of

ancilliary task being performed by the subject did. These results are discussed

in terms of product design and safety, and implications of the study

for methodological development are considered.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Consumer products ; human factors ; kitchen; ranges;

reaction time; safety; warning lights.

18. AVAILABILITY ^^^tfrTl imited

For Official Distribution. Do Not Release to NTIS

~1 Order From Sup. of Doc, U.S. Government Printing Office

WarfTineton. D.C. 20402. SD Cat. No. CI 3

| L^Drder From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

26

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

$3-75

U5COMM.DC 29042-P74